1. Field of the Invention
This invention generally relates to a method and apparatus for facilitating lytic therapy and more specifically to a method and apparatus for reperfusing a vessel occluded by a thrombosis by means of thrombolytic therapy.
2. Description of Related Art
Thrombolytic therapy is a form of lytic therapy that involves the infusion of a thrombolytic agent for dissolving a thrombosis and reperfusing a vessel. The therapy involves the surgical introduction of a perfusion tube, such as a catheter or infusion guidewire, into a patient. After a distal end of the perfusion tube is positioned in or proximate the thrombosis, the infusion of a lytic agent, such as urokinase, begins. Sometimes this infusion may be preceded by the injection of a bolus of another lytic agent, such as streptokinase, through the infusion tube.
Infusion continues for some interval of time. Intervals ranging from several hours to a day are common. Angiographic or other similar diagnostic imaging techniques are used periodically during the infusion. These techniques monitor the effectiveness of the therapy and determine clot lysis by the onset of blood flow through the vessel. If lysis has occurred, the infusion terminates. Otherwise the infusion continues until the next diagnostic imaging session. This cycle of infusion and diagnostic imaging continues until lysis occurs.
This procedure has several disadvantages. Both the introduction of the catheter and the monitoring of the effectiveness of the therapy require the use of surgical facilities and attendance of medical personnel for the duration of the therapy. Normally the infusion is terminated during any diagnostic imaging session. Diagnostic imaging is conducted periodically with intervals of twenty minutes to two hours being typical. Consequently, it is difficult to determine the precise time at which the infusion of the lytic agent should terminate. If a given diagnostic imaging session discloses that lysis is complete, it can only be said that lysis occurred some time after the prior diagnostic imaging session. Patient tolerance and facility demands may limit the frequency of such diagnostic imaging sessions. Any delay between lysis and the termination of infusion may involve the needless administration of the lytic agent.
An improved method and system for thrombolytic therapy and other forms of lytic therapy that overcome these problems is needed. It would be particularly desirable to develop a method and system for limiting the infusion of a lytic agent precisely to the interval and amount required for lysis. It also would be desirable to develop an alternative method of determining the onset of blood flow through a reperfused vessel that reduces patient trauma and reduces the utilization of surgical resources.
The following patents disclose medical diagnostic monitoring apparatus for measuring blood flow in vivo using ultrasonic measurement techniques:
U.S. Pat. No. 4,582,067 (1986) Silverstein PA1 U.S. Pat. No. 4,637,401 (1987) Johnston PA1 U.S. Pat. No. 4,733,669 (1988) Segal PA1 U.S. Pat. No. 4,771,788 (1988) Millar PA1 U.S. Pat. No. 4,869,263 (1989) Segal et al PA1 U.S. Pat. No. 4,947,852 (1990) Nassi et al
The Silverstein patent discloses a catheter used with an endoscope. The catheter supports a Doppler crystal transducer at its distal end. This catheter is dedicated to measuring in vivo blood flow for the purpose of identifying and monitoring intracorporeal biological structures for medical diagnosis.
The Johnston patent discloses diagnostic apparatus for measuring volumetric blood flow. The apparatus includes a Doppler transducer at a distal end of a catheter for being located in a vessel. Measurements are taken when a proximally located balloon is deflated or inflated. The measured flow rates under these balloon conditions is then converted into a volumetric flow rate.
Segal discloses a catheter with a Doppler crystal transducer adapted for measuring flow in a vessel with improved accuracy. The apparatus includes a wire that coacts with a vessel wall to position the Doppler transducer at an opposite vessel wall thereby to assure measurement at a predetermined position in the vessel.
In accordance with the Millar patent apparatus for measuring blood flow includes a guidewire with a central lumen that carries, in one embodiment, a steering wire. A Doppler crystal transducer is located at the distal end. This apparatus is adapted for measuring blood flow at various positions along an arterial tree. It is suggested that the lumen could be used for introducing chemicals or fluids, such as aneurism dye, into the blood stream.
The Segal et al patent discloses a catheter with multiple lumens and a distal ultrasonic transducer for measuring cardiac output. Readings of the transducer signals are taken when a balloon is inflated to different diameters.
Nassi et al disclose a catheter with multiple lumens that supports two transducers at its distal end. One of the lumens is identified as a right atrial pressure and injectate lumen. Nassi et al also disclose a console that displays blood flow and vessel diameter measurements. This apparatus provides an alarm if the blood flow or vessel diameter exceeds a minimum or maximum limit.
Although ultrasonic blood flow monitors in various forms have existed for over 20 years, they have been used as diagnostic tools. Even a suggestion of using the apparatus to inject a dye or the like occurs in the context of a diagnostic procedure. As these devices have matured, they have become more accurate, more complex and more expensive. They have not been adopted for therapeutic applications such as monitoring the onset of blood flow during thrombolytic therapy. Consequently, thrombolytic therapy has continued to rely on angiographic and other diagnostic imaging techniques notwithstanding the potential for additional patient trauma and demands on medical resources.